Due to their particular properties, laser light sources are increasingly replacing classical light sources. Compared to light-emitting diodes (LEDs), laser diodes (LDs) are particularly characterised in that the latter can be significantly more efficient and more powerful. In addition, by having a low spectral bandwidth and by means of the high spatial and temporal coherence of the emitted radiation, completely new fields of application can be tapped into. This is of particular relevance to the field of mobile devices (smartphones), as energy-efficient projection systems or high performance laser scanners, for example, can be integrated into said devices for scanning the surroundings.
However, for some applications LDs have a significant disadvantage over LEDs. Whereas LEDs are so-called surface emitters, the radiated light of which can be collimated and/or focussed by simple lenses, laser diodes are generally Gaussian emitters in which the spatial brightness distribution of the emitted light is described by a Gaussian distribution. However, in many cases it is preferable for illumination purposes to have a distribution of the intensity in the beam that is as homogenous as possible, so that here there often needs to be a complicated transformation of the beam profile into a rectangular profile (top-hat or flat-top). In laser scanners, however, sharp lines or grid profiles are often particularly preferred beam shapes.
In edge-emitting laser diodes a further complicating factor is that the beam profile emitted by the diode also often differs in horizontal and vertical direction (slow and fast-moving laser axis). For a mutual adjustment of both said axes additional cylindrical lens arrangements are often therefore required in the beam path. However, such a beam shaping or transformation may also be necessary with other laser light sources. For example, surface-emitting laser diodes can also have a very inhomogeneous radiation profile. This then must also be adjusted in a laborious manner by suitable lenses according to the respective requirements.
In U.S. Pat. No. 7,532,651 B2 an illuminating system for optical modulators is described, in which a phase plate and a lens are used for the efficient illumination of a microelectromechanical (MEMS) modulator array by beam transformation. However, such an arrangement is only suitable to a limited degree for integration into inexpensive mobile devices, as here a plurality of optical components with a corresponding space requirement have to be combined with one another to fit as accurately as a possible. When using lenses in a lighting system, a miniaturisation of the corresponding assembly is substantially limited by the focal lengths of the individual lenses. However, in addition to the total length of the beam path, lenses also have the disadvantage that their surfaces have to be made anti-reflective at great expense to avoid scattering effects. In this way the spectral properties of the optical system are often significantly limited, so that the use of the latter is set to specific wavelength ranges. In addition, in some applications particular demands are also made of the quality of the individual surfaces, their tempering and the applied coatings, which is reflected in the manufacturing costs and also the cost of construction. Additionally, the requirements relating to the centricity of the beam path and the long-term stability of the individual assembly are typically problematic for the integration of optical elements into compact mobile devices. For example, when using inexpensive plastic lenses, if there is a change in the operating temperature of the device a significant variation in the effective focal length of the lens is often noted. The reason for this is in particular that the refractive index of optical plastic materials is relatively temperature-dependent and therefore it is possible in the temperature ranges common for such devices that much more noticeable mapping errors may occur.
Therefore, the objective of the invention is to provide a projection system for generating spatially modulated laser radiation with an optical arrangement for transforming the radiation of a single mode laser, which avoids one or more of the said problems of the prior art on transforming beam profiles for lighting purposes or at least significantly reduces the latter. In particular, a projection system for generating spatially modulated laser radiation can be provided with an optical arrangement for the transformation of the radiation of a single mode laser, which enables a particularly compact and robust structure with a minimum number of optical components, wherein the optical properties are supposed to be stable over a broad temperature range and the useable wavelength range is not restricted by additional anti-reflective coatings.